FILE: A man with an umbrella crosses the street next to a cable car on California Street during rainy weather in San Francisco on Dec. 20, 2023. 

A blast of post-storm cold air is sweeping across the Bay Area, causing some of the coldest temperatures of the month — as inland valleys dip into the low 30s. 

After a day of gusty winds, scattered showers and small hail, forecasters say the real headline now is the temperature drop.

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North Bay and East Bay valleys fell to lower 30s by early Friday morning. Temperatures Friday night into Saturday morning are expected to remain cold, generally in the low to mid-30s in those same inland areas, before a more noticeable warmup arrives late in the weekend.

A cold weather advisory and extreme cold warning are in effect for portions of the region early Friday, according to the weather service’s forecast discussion. Forecasters cautioned that damp ground combined with subfreezing temperatures could create slick spots in some locations.

On Thursday, a sharp cold front moved through the Bay Area, producing gusts between 40 and 50 mph along the coast and across higher elevations, with some locations briefly exceeding 60 mph. 

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“The wind chill values are lower due to the wind speed, but the wind chill values aren’t forecast to be that much lower as the winds are going to relax,” said Roger Gass, a meteorologist with the National Weather Service.

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Looking ahead, forecasters expect temperatures to rebound Sunday.

“We are expecting a significant warmup into the lower 40s, lower to mid-40s on Sunday, as we start to get deeper moisture from a potential atmospheric river approaching the region,” Gass said.

Showers are forecast to sweep into the North Bay by Saturday morning. Farther south, precipitation is expected to be lighter and more intermittent, with patchy drizzle possible in the central and southern parts of the region.

By Monday, a low-pressure system positioned off the Pacific Northwest is forecast to draw in subtropical moisture, increasing rainfall potential across the Bay Area. Current projections call for widespread rain from Monday into Tuesday, with the possibility of minor flooding in low-lying and poorly drained areas. Ponding on roadways and slick travel conditions are likely.

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Despite the cold snap, no record lows are forecast to fall. Napa is expected to reach about 30 degrees Friday morning, above its record of 27 degrees set in 2018. Livermore is forecast near 30 degrees, above its 27-degree record set in 2018. San Francisco is forecast to bottom out near 42 degrees, above its record low of 38 degrees set in 1897.

“There may be several sites that get close, but we’re not anticipating currently any records to be broken,” Gass said.

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